The warning comes after a sea battle Thursday left at least 19 Sri Lankan forces and an unknown number of militants dead.

It was the bloodiest military confrontation since the 2002 truce that ended two decades of civil war.

The fighting broke out about 50 kilometers (30 miles) north of the northern port city Point Pedro in the Jaffna peninsula.

Navy fast attack craft were escorting the passenger liner Pearl Cruiser, which held more than 700 troops returning to their assignments in the north. In initial reports, navy officials said a flotilla of more than 20 rebel boats attacked.

During the three-hour battle, officials said, at least three navy fast attack craft escorted the passenger vessel into Indian territorial waters, where the Indian Coast Guard offered protection. The ships later returned to the Northern Area Naval Base in Kankesanthurai.

Earlier in the day, Sri Lanka's air force began bombing rebel areas in the northern Wanni region.

A newly built rebel air strip was one bombing target, air force sources said. The pro-Liberation Tigers of Tamil Eelam (LTTE) Web site Tamilnet confirmed the bombing raids.

The Sri Lankan army also has begun artillery attacks on rebel positions in the northeastern port city of Trincomalee, military officials reported.

A cease-fire brokered by Norway in 2002 has broken down in recent weeks after rebel attacks and government reprisals against Tamil strongholds.

LTTE rebels have been seeking their own homeland in the north and east of the island nation, which lies to the south of India.

More than 65,000 people on both sides have been killed since the LTTE began fighting in 1983 to create a separate state for Sri Lanka's 3.2 million Tamils, alleging discrimination by the country's 14 million Sinhalese.